Rotating electric machines used for driving a vehicle are particularly desired to be downsized and to have higher output as compared with ordinary rotating electric machines. In a stator of a rotating electric machine, by using, as a coil, a segment coil conductor having a large cross-sectional area, it is possible to raise the space factor of the conductor in a slot of a stator core, thereby achieving downsizing and higher output. In a slot of a stator core, a plurality of segment coil conductors are inserted on an inner circumferential side and an outer circumferential side. Furthermore, a slot insulating paper is inserted between the segment coil conductors adjacent to each other in a direction from the inner circumference to the outer circumference and between the respective segment coil conductors and the stator core. The slot insulating paper is required to have a sufficient shape and area to ensure insulating property. In addition, it is preferable to have a thickness as thin as possible in order to raise the space factor of the conductor.
As a slot insulating paper inserted in a slot of a stator core, there is known a slot insulating paper which is formed into a substantially B-letter shape covering an outer circumference of each segment coil conductor and having an overlapping portion between adjacent segment coil conductors (for example, see PTL 1). In this structure, the slot insulating paper having a substantially B-letter shape is inserted into each slot of the stator core in advance. A segment coil conductor is inserted therein (for example, see PTL 1).